IETF RFC 2227 PDF

This document proposes a simple extension to HTTP, using a new "Meter" header, which permits a limited form of demographic information (colloquially called "hit-counts") to be reported by caches to origin servers, in a more efficient manner than the "cache-busting" techniques currently used. It also permits an origin server to control the number of times a cache uses a cached response, and outlines a technique that origin servers can use to capture referral information without "cache-busting."